Use of link aggregation enables bundled-manner handling of a plurality of physical lines (links) as a single logical line. For example, it is assumed that a communication device A and a communication device B are coupled with each other by ten physical lines having a band of 1 gigabits per second (Gbps). In this case, the ten lines which connect the communication device A and the communication device B may be dealt with as a single line of 10 Gbps.
As a related technique, a routing method for a case in which routers are directly coupled with each other with a plurality of connections has been disclosed. In this method, a router which receives a frame extracts one or a plurality of pieces of header information. Then, an output interface of the frame is decided by using the extracted information as a key. Therefore, frames having identical information serving as a key (identical flows) are outputted from the same interface, being able to avoid order reverse of frames.
Such method that a plurality of logical channels which designate a communication route are set between two nodes, and a transmission node divides transmission information into a plurality of frames and provides sequence numbers to respective frames so as to transmit the frames in a manner to distribute the frames to a plurality of logical channels has also been disclosed. A reception node synthesizes the frames which are transmitted in a manner to be distributed to a plurality of logical channels, by using the sequence numbers, thus restoring the transmitted information.
As related art, Japanese Laid-open Patent Publication No. 2000-13439, Japanese Laid-open Patent Publication No. 6-276230, and the like are disclosed, for example.
Even if a logical bandwidth is expanded by using the link aggregation, in a case in which a link used for transmission of a frame is uniquely decided by associating the link with a destination and a source of the frame, frames are outputted to an identical link when combinations of destinations and sources of the frames are the same as each other. Therefore, it is difficult to transmit a flow exceeding a bandwidth of a physical link even a flow which is able to be transmitted and received in a band narrower than a band which is logically obtained by the link aggregation. If it is possible to distribute frames which are included in a flow of the same combination of a destination and a source to a plurality of physical links, it is possible to transmit a flow equal to or larger than a bandwidth of a physical link. However, a usage condition varies depending on a physical link, so that order reverse of frames may occur. Further, in a case in which sequence numbers are provided to respective frames, a region for storing a sequence number is secured in each of the frames and therefore, a format of a frame transmitted from a terminal is changed. Thus, there is no versatility.